Were australopithecines ape--human intermediates or
just apes? a test of both hypotheses using the "Lucy"
skeleton.

Abstract:

Mainstream scientists often claim that australopithecines such as
the specimen nicknamed "Lucy" exhibit anatomy intermediate
between that of apes and that of humans and use this as evidence that
humans evolved from australopithecines, which evolved from apes. On the
other hand, creationists reject evolution and claim that
australopithecines are "just apes." Here, a point-by-point
visual comparison with the skeletons of a chimpanzee, "Lucy,"
and a human is presented in order to evaluate both claims, treating them
as testable hypotheses. The results support the hypothesis that
australopithecines are anatomically intermediate between apes and
humans. Classroom applications of this test of hypotheses are also
discussed.

To effectively introduce the evidence for evolution, it is
important that a biology teacher have a basic grasp of the anatomy of
australopithecines. This is because the presence of evolutionary
sequences in the fossil record is one of the main lines of evidence for
evolution, and no fossil evolutionary lineage generates more interest
than our own. As evolutionary intermediates between apes and humans, the
australopithecines form a prominent part of that lineage, and their
anatomy is a beautiful illustration of the anatomical transition from
ape to human.

A good way to become familiar with australopithecine anatomy would
be to use a point-by-point comparison of their skeletons with those of
apes and humans. Unfortunately, such is lacking in most biology
textbooks (e.g., Starr & Taggart, 2004; Campbell et al., 2009),
including those on evolution (e.g., Volpe & Rosenbaum, 2000; Barton
et al., 2007). This makes it difficult for the biology teacher to
illustrate exactly how australopithecines are intermediate between apes
and humans. Here, I compare an australopithecine skeleton with those of
the chimpanzee (Pan troglodytes) and the modern human species (Homo
sapiens).

A point-by-point comparison of ape, australopithecine, and human
anatomy presents another opportunity that should be seized. Such a
comparison can be used to test two competing claims that can be treated
as testable hypotheses: (1) the consensus among mainstream scientists
that australopithecine anatomy is intermediate between those of apes and
humans and (2) the young-earth creationist claim that australopithecines
are "just apes," unrelated to humans (Mehlert, 2000; Line,
2005; Murdock, 2006). In a time of rampant creationism (Mazur, 2005;
Miller et al., 2006), it is important not to dismiss the latter claim
out of hand but to explicitly put it to the test.

Hundreds of australopithecine specimens are known, but to keep this
study simple and to avoid overwhelming the nonspecialist reader, I chose
to use a single australopithecine specimen: AL 288-1, nicknamed
"Lucy." Discovered in Ethiopia in 1974 (Johanson et al.,
1982), AL 288-1 is particularly appropriate to use for this test of
hypotheses, for several reasons. First, at 40% complete (Johanson et
al., 1982), it is one of the most complete australopithecine skeletons
known to date; most of the skull is missing, but the preserved portions
of the jaw, dentition, vertebral column, pelvis, and limbs are
sufficient to test the two hypotheses with traits from a variety of
skeletal regions. Second, cast replicas of the entire known skeleton of
Lucy are commercially available--as are those of chimpanzees and
humans--so this test of hypotheses can be repeated by any academic or
other entity with an appropriate budget without having to travel to see
the fossil itself. Third, AL 288-1 represents a species,
Australopithecus afarensis, with important phylogenetic significance. It
predates both our own genus (Homo) and the later australopithecines with
which early Homo coexisted, and it is possibly ancestral to both (Stein
& Rowe, 2006). Other specimens of A. afarensis show that AL 288-1 is
similar enough to its conspecifics to serve as an exemplar of the
species (Drapeau et al., 2005). Fourth, it is a particularly famous
fossil, and the public's familiarity with it continues to increase
as a result of publicity generated by its current tour through the
United States.

The hypothesis that Lucy is anatomically intermediate between apes
and humans predicts that a point-by-point comparison will reveal a
mixture of apelike features and humanlike features in the specimen. The
hypothesis that Lucy is just an ape predicts that such a comparison will
only reveal apelike features in the specimen. Some proponents of the
latter hypothesis recognize that australopithecines had upright bipedal
locomotion but do not consider this a feature linking australopithecines
with humans (Mehlert, 2000; Murdock, 2006). To satisfy such strict
interpreters of the "just an ape" hypothesis, the predictions
can be modified: the hypothesis that Lucy is anatomically intermediate
between apes and humans predicts that a point-by-point comparison will
reveal in Lucy a mixture of apelike features and humanlike features in
which some of the humanlike features are not necessary for upright
bipedal locomotion. The hypothesis that Lucy is just an ape predicts
that the comparison will reveal no humanlike features in Lucy that are
unnecessary for upright bipedal locomotion.

* Materials & Methods

To test the hypotheses, I compiled a list of skeletal differences
between chimpanzee and human skeletons, using direct examination of
several chimpanzee skeletons at the U.S. National Museum and human
skeletons at Fayetteville State University and the U.S. National Museum.
I examined the australopithecine skeleton AL 288-1, which was on
temporary display in Seattle, and tabulated which characters in the list
exhibit the apelike state and which exhibit the humanlike state (Figures
1 and 2, Table 1). For features that I could not make out on AL 288-1
because of the position of the specimen as it was laid out for display,
I used a cast of the specimen.

[FIGURE 1 OMITTED]

* Results & Conclusion

Of 36 anatomical characters examined on AL 288-1, 14 (39%) exhibit
the apelike state and 22 (61%) exhibit the humanlike state. Of the 22
characters for which AL 288-1 exhibits the humanlike state, 12 (55%) are
found on the vertebral column, pelvis, and lower limb and could
therefore be construed as related to upright bipedal locomotion, whereas
10 (45%) are found on the jaw, teeth, and upper limb and are therefore
unrelated to upright bipedal locomotion. The data therefore support the
hypothesis that Lucy is anatomically intermediate between apes and
humans and falsify the hypothesis that Lucy is just an ape.

* Discussion

This study can be adapted as a classroom exercise using
commercially available casts of the Lucy skeleton in conjunction with
chimp and human skeletons or commercially available casts thereof (Table
2). For schools with lower budgets, pictures could be used instead of
casts. Free images of human and chimpanzee bones in various views are
available at http://www.eskeletons.org. Bone Clones
(http://www.boneclones.com) sells a 14" x 11" poster of the
Lucy skeleton for $10.00, although it shows the bones in only one view.

[FIGURE 2 OMITTED]

One way to adapt this study to the classroom is for a teacher to
instruct students to come up with their own lists of differences between
chimp and human skeletons and then run down the list with the Lucy
skeleton to tabulate traits for which it exhibits the apelike state and
those for which it exhibits the humanlike state. Alternatively, the
teacher could instruct students to focus their attention on the traits
used here (Table 1). Either way, at the end of the exercise, students
can be asked to make up their own minds about whether Lucy is
anatomically intermediate between apes and humans or not.

A potential criticism of such an exercise is that it does not
employ a cladistic approach. Cladistics, the preferred method for
determining relationships, uses shared, derived characters (traits) to
determine which taxa are most closely related to which, ignoring shared
ancestral characters. It treats all taxa as endpoints on an evolutionary
tree rather than treating any taxon as ancestral to any other. By
contrast, the approach used here treats "apes" (exemplified by
the chimpanzee) as an ancestral grade from which
"australopithecines" evolved and treats
"australopithecines" (exemplified by Lucy) as an ancestral
evolutionary grade from which humans evolved. Such a way of looking at
things is accurate but may confuse students that have been taught in a
strictly cladistic manner. It is therefore important for the teacher to
note that the results of this exercise do not show that the chimp is the
ancestor of Lucy and that Lucy is the ancestor of humans. Instead, the
results show that a representative of the australopithecine grade (Lucy)
has too many anatomical traits in common with humans--and in contrast
with apes--to support a conclusion that the creature is a mere ape.

A classroom exercise such as this can be taken a step further by
noting functional implications of Lucy's anatomy as well as the
anatomy of the chimp and the human. Table 3 lists functional hypotheses
associated with locomotion and predictions that are testable with the
Lucy material. For this, students should be instructed to compare each
specimen's anatomy with the predictions of each hypothesis to
determine which hypotheses are falsified (or not) by anatomical data.
Such an exercise not only elucidates australopithecine locomotion but
also involves the use of hypothesis testing, an important scientific
tool.

Exercises such as these are not likely to change the mind of anyone
who is strongly influenced by the religious dogmas that keep young-earth
creationism alive. Nevertheless, they are potentially useful for
students on both sides of the fence. For those who accept that humans
evolved from apelike precursors, such exercises provide clarification of
the evidence. For those who do not accept the evolution of humans from
nonhumans, such exercises at least show that the idea is not just a
baseless atheistic conspiracy, as is often falsely claimed (Gish, 1995;
Sarfati, 2002), but is instead based on observable physical data.

DOI: 10.1525/abt.2010.72.2.4

* Acknowledgments

Linda Gordon and Jennifer Clark of the U.S. National Museum deserve
thanks for access to chimpanzee skeletons and a cast of AL 288-1,
respectively. I also thank Jennifer Muench for her assistance, Rick
Johnson and Marilyn Jacobs for lodging in Seattle, and Scott and Lynn
Rountree for lodging in Washington, DC. Finally, I thank two anonymous
reviewers for constructive comments that improved the manuscript.

Table 1. Comparison of chimpanzee (Pan troglodytes) and modern human
(Homo sapiens) skeletal anatomy. Underlining shows the condition in
"Lucy" (Australopithecus afarensis, specimen AL 288-1).
Anatomical Trait Condition in Condition in Modern
Chimpanzee Human
1. Shape of mandible V-shaped parabolic
2. Simian shelf of present absent
mandible
3. Slope of strongly sloped vertical
mandibular symphysis (receding
in lateral view inferiorly)
4. Protruding chin absent present
5. Orientation of parallel to each posteriorly
left and right other divergent
postcanine tooth
rows
6. Incisor size about the same as much smaller than
molar size molars
7. Diastema present absent
(toothless space)
between lower canine
and first lower
premolar
8. Lateral facet for present absent
canine on first
lower premolar
9. Size of first much larger than about the same size
lower premolar second premolar as second premolar
10. Spinous process angled angled
of 4th through 10th 20-45[degrees] 50-90[degrees]
thoracic vertebrae toward tail toward tail
11. Transverse angled dorsally angled dorsally
processes of 10th about 30[degrees] 50-80[degrees]
through 12th
thoracic vertebrae
12. Displacement of
postzygapophyses absent present
beyond caudal margin
of centrum on 11th
and 12th thoracic
vertebrae
13. Spinous process angled toward tail; not angled toward
of 2nd and 3rd trapezoidal tail; square
lumbar vertebrae
14. Transverse width not much greater much greater than
of centrum of 2nd than length or its length and
through 5th lumbar height of centrum height
vertebrae
15. Number of fused six five
vertebrae in sacrum
16. Maximum about 2/3 the length about equal to
transverse of the sacrum length of sacrum
(side-to-side) width
of sacrum (not
counting 6th sacral
vertebra of chimp)
17. Lateral prominent weak
supracondylar ridge
of humerus
18. Lateral prominent weak
epicondyle of
humerus
19. Shafts of radius strongly bowed straight
and ulna
20. Proximal present absent
extension of
olecranon process of
ulna
21. Medial margin of concave straight
capitate (the carpal
bone at the base of
finger III)
22. Arching of present; bones no arching; bones
metacarpals and concave on palmar straight
manual phalanges surface
23. Orientation of wings stick straight wings curve around
wings of ilium out to the sides toward the belly
24. Dimensions of much taller than height and width
ilium beyond wide about equal
acetabulum (hip
socket)
25. Shape of greater a broad, shallow a narrow, tight
sciatic notch curve curve
26. Orientation of acetabulum faces acetabulum faces
acetabulum straight out somewhat laterally
laterally and somewhat
anteriorly
27. Diameter of approximately equal greater than
femoral head to diameter of diameter of femoral
femoral shaft in shaft in anterior
anterior view view
28. Orientation of
greater trochanter
extends straight
proximally
tip is curved
medially
29. Height of tip of level with femoral does not extend as
greater trochanter head when femoral far proximally as
shaft is vertical femoral head when
femoral shaft is
vertical
30. Middle part of slanted perpendicular to
distal margin of shaft
tibia in posterior
view
31. Transverse width greater than 1/3 less than 1/4
of medial malleolus transverse width of transverse width of
of tibia entire distal end of entire distal end of
tibia tibia
32. Lateral rectangular diamond-shaped
malleolus of fibula
in lateral view
33. Distal process angled medially extends straight
of talus (tarsal distally
bone that supports
the tibia)
34. Medial process present absent
of talus medial and
plantar to tibial
facet
35. Arching of present; bones absent; bones
metatarsals and of concave toward sole straight
pedal phalanges
other than distal
phalanx
36. Shape of convex concave
proximal margin of
proximal phalanx of
toes I-III in
lateral view
Table 2. Commercially available casts of skeletons of chimpanzee,
human, and "Lucy" (AL 288-1). Listed are the least expensive casts
of which the author is aware.
Cast Price (USD) Vendor
"Lucy": mounted skeleton $6300.00 Bone Clones
"Lucy": disarticulated $1900.00 Bone Clones
skeleton
Chimpanzee: mounted $2900.00 Bone Clones
skeleton
Chimpanzee: $1700.00 Bone Clones
disarticulated skeleton
Human: mounted skeleton $359.00 Anatomical Chart Company
Human: disarticulated $163.95 Anatomical Chart Company
skeleton
Table 3. Functional hypotheses regarding the chimpanzee, the human,
and "Lucy," and their anatomical predictions.
Hypothesis Predictions
The creature habitually walks 1. Thoracic and lumbar centra
quadrupedally, with its back are of similar size.
horizontal.
2. The head-to-tail length of
the ilium is much greater than
its transverse (side-to-side)
width.
The creature habitually walks 1. Lumbar centra are larger
bipedally, with its back (especially in cranial and
vertical. caudal views, the views from the
head and from the tail
respectively) than thoracic
centra.
2. The head-to-tail length of
the ilium is similar to its
transverse width.
The ability of the creature's 1. The metacarpals, metatarsals,
fingers and toes to grasp and phalanges are curved
branches is enhanced. (concave toward the palm/sole).
The ability of the creature's 1. The metacarpals, metatarsals,
fingers and toes to grasp and phalanges are straight.
branches is reduced.
The creature's capacity for 1. The radius and ulna are
brachiation (locomotion by strongly curved.
using the hands to grasp
branches while the body hangs 2. The length of the humerus +
beneath, like a human child on forearm (radius and ulna) is
playground "monkeybars") is greater than that of the femur +
enhanced. tibia.
The creature's capacity for 1. The radius and ulna are
brachiation is reduced. straight.
2. The length of the humerus +
forearm is similar to or less
than that of the femur + tibia.